4) install the OVID manager (GUI-console) on your PC / workstation. I used Windows. It is available for Windows. If you do not have windows, you can edit the XML files directly (good luck)
5) in the ovid manager, create a new project, add your ovid, and start creating adapters. For each possible DB domain, you must create one adaptor, for example if you try to tnsping LSC01.PROD.DB and you have the description stored as cn=lsc01, cn=oracleContext, cn=PROD.DB, ou=tns, ou=appl, dc=lcsys, dc=ch you will need have

This should work. Not sure if you will like OViD, the interface is pretty awful.

Also it is not too flexible, you need to add an adaptor for each db domain. Still better than providing a TopDomain for each DB Domain with anonymous access to root.

Yes, one more point, tns client access the ldap anonymously, so OViD does help to improve security, you set anonymous access to your OViD, you disable ACI on your OViD, and you use a credential to log in to your LDAP. It is safer, because you use a remoteBase, so anonymous access is granted only to that branch of your directory.